1. Field of the Invention
The present invention relates to a method of welding and a steel plate deck.
Priority is claimed on Japanese Patent Application No. 2007-186047, filed Jul. 17, 2007, the content of which is incorporated herein by reference.
2. Description of Related Art
A steel plate deck is known as a flooring material used for buildings such as bridges. A steel plate deck is constituted of a deck plate (steel plate) and a plurality stiffeners (ribs) arranged on the deck plate, and the deck plate and the ribs are integrated with each other by longitudinal welding (Japanese Unexamined Patent Application, First Publication, No. 2003-183769; Japanese Unexamined Patent Application, First Publication, No. H08-281476; Japanese Unexamined Patent Application, First Publication, No. 2003-080396). Closed-section ribs, steel members having V-shaped or U-shaped closed sections are known as examples of the ribs. In the welding of the closed-section ribs and deck plate, an amount of penetration of the weld zone is required to be not less than 75% of the plate thickness of the ribs. In some cases, the amount of penetration of the weld zone is required to be not less than 80% of the plate thickness of the ribs.
Full-penetration welding using a backing metal, gas-shielded metal arc welding, and submerged arc welding are generally known methods of welding. Particularly, full-penetration welding is known as an effective method in that a high amount of penetration is stably ensured.
On the other hand, in the case of welding of a deck plate and a closed section rib, it is difficult to perform full-penetration welding since the structure of the closed-section ribs makes it difficult to use a backing metal. Therefore, gas-shielded metal arc welding, submerged arc welding or the like have conventionally been used in the welding of the deck plate and the closed-section rib. In such methods, welding is performed while edges of the closed section ribs are made to contact the deck plate. A portion of an edge of each rib, which is made to contact the deck plate, is called a root portion.
In general, the edge of the rib has a root portion which is cut to have an orthogonal or nearly orthogonal angle. Therefore, when the edge of the rib is made to contact the deck plate, only the root portion is in contact with the deck plate, forming a clearance (groove) corresponding to a setting angle between the deck plate and the edge of the rib.
When the welding is performed in that state, there is a case in which molten slag generated during the welding intrudes into the groove. In addition, blowholes are easily formed by the gas generated during the welding. When the molten slag and the blowholes generated during the welding intrude to an extent deeper than the target amount of penetration, the molten slag and blowholes remain in those states. The residual slag and blowholes cause slag inclusion and/or insufficient amount of penetration.
Japanese Unexamined Patent Application, First Publication No. H08-281476 describes a flux cored wire for gas-shielded metal arc welding. By means of the limited composition of the wire, it is possible to obtain a bead for providing satisfactory form and appearance of the weld zone. Japanese Unexamined Patent Application, First Publication No. 2003-80396 describes a technique for obtaining a deep penetration by limiting the filling factor of the flux in addition to the limitation of the composition of the wire. However, there are still problems in that the slag inclusion in the root portion cannot be completely prevented, and a stable penetration cannot be achieved.
In a technique proposed as a solution for these problems, generation of the above-described defects is avoided by increasing the amount of penetration such that the melting proceeds to a position deeper than the position of intrusion of the molten slag and the blowholes. However, the increased amount of penetration sometimes results in excessive melting that reaches the back surface (inner surface of the U-shaped member) of the closed section ribs, thereby making it difficult to control a stable amount of penetration, and causing unstable forms of beads.